1. Field of the Invention
The present invention relates to digital mobile telecommunication systems and, more particularly, to a transmitter with increased throughput of user information between a mobile telecommunication terminal and a base station.
2. Description of the Related Art
A Code Division Multiple Access (CDMA) system sets an n-bit random pattern (spread code) of xe2x80x9c0sxe2x80x9d and xe2x80x9c1sxe2x80x9d and transmits a message stream of that pattern and an inverted pattern at a bit rate n times the message bit rate. As the CDMA system transmits a message at the high bit rate, the width of the frequency spectrum is spread. Therefore, the CDMA system is sometimes referred to as a spread spectrum system.
A mobile telecommunication terminal, which is a subscriber or personal communication terminal, provides telecommunication services for the user by radio communication with a base station.
A conventional transmitter of the mobile telecommunication terminal and the base station in a typical CDMA system is illustrated in FIG. 1. The transmitter includes a voice encoder 10, a Cyclic Redundancy Check (CRC) encoder 12, a tail bit inserter 14, a Forward Error Correction (FEC) encoder 16, an interleaver 18, a symbol repeater 20, and a digital modulator 22.
In operation, voice or data information coded by voice encoder 10 is applied to CRC encoder 12 and tail bit inserter 14. The CRC encoder 12 CRC-encodes the applied voice or data information and adds the CRC-encoded result to the voice or data information. The tail bit inserter 14 inserts tail bits (fixed value bits) into the applied voice or data information. The CRC encoder 12 and tail bit inserter 14 perform the above operations in the time unit of a frame. The CRC-encoded result and the tail bits are added to the voice or data information to detect a transmission error of a traffic channel frame upon transmitting or receiving traffic channel data in the time unit of a frame.
Referring to FIG. 2, the structure of a traffic channel frame in which the CRC-encoded result and the tail bits are added to the voice or data information by CRC encoder 12 and tail bit inserter 14 is shown. The traffic channel frame is comprised of I data (voice) bits corresponding to the voice information generated by voice encoder 10, F CRC bits generated by CRC encoder 12 via a polynomial which uses the voice information bits, and T tail bits consisting of xe2x80x9c0sxe2x80x9d.
For example, in an IS-95 system, a traffic channel frame of 9600 bps voice data is comprised of 192 bits during a frame of 20 ms in duration. The 192 bits are employed as follows: 172 voice information bits, 12 CRC bits, and 8 tail bits. A traffic channel frame of 4800 bps voice data is comprised of 96 bits during a frame of 20 ms. The 96 bits are employed as follows: 80 voice information bits, 8 CRC bits, and 8 tail bits.
The traffic channel frame illustrated in FIG. 2 is applied to an Radio Frequency (RF) transmitter after being processed by FEC encoder 16, interleaver 18, symbol repeater 20 and digital modulator 22, and carrier-modulated.
The FEC encoder 16 is a convolutional encoder for correcting a bit error in the receiver generated during radio transmission. The interleaver 18 is a block interleaver that performs interleaving to prevent a burst error which may be generated on a mobile telecommunication radio transmission channel. The symbol repeater 20 adjusts the symbol rate of the interleaved traffic channel frame. The digital modulator 22 consists of a direct sequence (DS) spread spectrum device, a data modulator, and a digital low pass filter for increasing the efficiency of a frequency band.
Meanwhile, the receiver receives the traffic channel frame and corrects an error through a digital demodulator, a de-interleaver, and a Viterbi decoder having a FEC decoding function. The error-corrected voice information is applied to a CRC encoder which is identical to that used in the transmitter. The receiver compares CRC bits obtained by the CRC encoder with CRC bits within the received traffic channel frame. If they are equal to each other, then no errors are considered to be present in the transmitted traffic channel frame. However, if they are not equal, then an error(s) is considered to be present in the traffic channel frame.
Thus, the CRC bits are inserted into the traffic channel frame together with the voice information in order to determine whether or not there are errors in the traffic channel frame. As such, the throughput of the voice information is decreased by a number of bits equal to the number of CRC bits. For instance, in the IS-95 system of 9600 bps voice data, since there are 12 CRC bits out of the total 192 bits during the frame time of 20 ms, the throughput of the voice information decreases by 6.25 percent (i.e., 12/192xc3x97100). Similarly, in the IS-95 system of 4800 bps voice data, the throughput of the voice information decreases by 8.33 percent (i.e., 8/96xc3x97100).
It is an object of the present invention to provide a transmitter for increasing the throughput of traffic information in a mobile communication system by transmitting CRC bits through a control channel frame.
It is another object of the present invention to provide a method for increasing the throughput of traffic information in a mobile communication system by transmitting CRC bits through a control channel frame.
In one aspect of the invention, a transmitter for increasing information throughput in a digital mobile telecommunication system is provided. The transmitter includes: means for implementing error correction with respect to a traffic channel frame having user service information to generate CRC bits for the user service information of the traffic channel frame; and means for inserting the CRC bits into a control channel frame, wherein the traffic channel frame and the control channel frame having the inserted CRC bits are transmitted at a radio frequency.
In another aspect of the invention, a method for increasing information throughput in a transmitter of a digital mobile telecommunication system is provided. The method includes the steps of: implementing error correction with respect to a traffic channel frame having user service information to generate CRC bits for the user service information of the traffic channel frame; and inserting the CRC bits into a control channel frame, wherein the traffic channel frame and the control channel frame having the inserted CRC bits are transmitted at a radio frequency.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.